1. Field of the Invention
The present invention relates to the manufacture of battery assemblies, and more particularly solid state batteries maintained in a protective material to exclude air, water and other gasses to protect the battery against physical abuse to increase its shelf life. The battery assembly is produced by surrounding solid state battery components with an enveloping material and sealing the edges of the material around the components in a vacuum environment.
2. Description of the Prior Art
Presently there is a high level of interest in industry in designing thin layer solid state batteries, particularly lithium anode cells. These batteries include a lithium anode, a transition metal oxide polymer composite cathode, and a solid or liquid electrolyte which includes a dissolved lithium salt. Examples of such batteries are set forth in U.S. Pat. Nos. 4,303,748 to Armand, 4,589,197 to North, 4,228,226 to Christiansen and U.S. patent application Ser. Nos. 238,071, filed Aug. 30, 1988; 115,492 filed Oct. 30, 1987; and 173,385 filed Mar. 25, 1988.
A principal object of these batteries is to make them as thin and compact as possible while still satisfying market needs in terms of storage capacity, current density, shelf-life and the like.
A problem in achieving this object resides in the fact that these batteries must be moisture impermeable as some of the components are very hygroscopic and can absorb water and gasses which can ruin the battery in less than a few hours. Additional problems have included accessing current from the battery once the components of the battery have been sealed, and the inability of such batteries to withstand the rigors of transportation, insertion and use into products.
Attempts have been made in the art to remedy some of the above described problems. For example, U.S. Pat. No. 4,502,903, assigned to Polaroid teaches the construction of the anode and cathode assemblies prior to sealing in a controlled atmosphere that is relatively inert to lithium and free of water, e.g. in dry air at a relative humidity of not more than 1 to 2 percent. This patent also teaches sealing of the edges of the battery unit under vacuum by heat and pressure.
U.S. Pat. No. 4,756,717, also assigned to Polaroid teaches the sealing of the battery component edges, under vacuum with the aid of heat and pressure. The sealed battery is assembled on a card stock base and is overwrapped with a layer of inert, chemically stable material which serves primarily to prevent mechanical interference with underlying components during the early stages of construction of the battery At a later stage of construction, this overwrap layer is sealed under a vacuum using heat and pressure Examples of overwrapping materials include polyethylene, paper, glassine and paper-foil laminates. This arrangement is taught with respect to a LeClanche cell.
Although the above described batteries alleviate some problems, they are deficient with respect to nonaqueous cells as they provide limited protection against environmental contamination, particularly at the areas of sealing Accordingly, there exists a need in the art for a battery which is stable for extended periods of time and is resistant to mechanical shock or water or air degradation.